1. Field of the Invention
The present invention relates to a linear actuator, and more particularly to a transmission device, which can be radially restricted but performs a stable axial extending/retracting movement.
2. Description of the Prior Art
The existing linear actuators have a quite wide range of use and are generally driven by motors to retract and extend other mechanisms.
Referring to FIGS. 1-2, a conventional linear actuator 90 disclosed in U.S. Pat. No. 6,880,416 is disposed with a three-segment telescopic structure consisting of three tubes 91, 92 and 93, in which is disposed a motor 94. The motor 94 is used to drive a screw assembly 95 which is disposed with three screws 96, 97 and 98. The three screws 96, 97 and 98 are connected to the respective tubes, 91, 92 and 93 of the linear actuator 90, respectively. The motor 94 drives the three screws 96, 97 and 98 to move in the axial direction, so that the respective tubes 91, 92 and 93 can be driven to retract and extend.
The above configuration and structure can retract and extend, but it still has the following disadvantages:
1. Complicated structure and inconvenient to assemble: the three screws 96, 97 and 98 push the respective tubes 91, 92 and 93 of the linear actuator 90, respectively, the three-segment screw structure complicates the linear actuator 90 and makes its assembly inconvenient.
2. High cost: the respective tubes 91, 92 and 93 of the above linear actuator 90 are connected to three screws 96, 97 and 98, respectively, such a structure design increases the cost of manufacturing the linear actuator 90.
Additionally, referring to FIGS. 3-4, another conventional actuator 80 disclosed in EP. Pat. No. 0982018 comprises a circular three-segment telescopic tube-shaped structure including three tubes 81, 82 and 83, in which are disposed a motor 84 and a screw 85. The motor 84 and the screw 85 are disposed in the tube 81, and the motor 84 drives the screw 85 to rotate. The screw 85 drives a brace rod due to threaded connection, and the brace rod is disposed with a pulley 86 on the top thereof, thus causing an axial displacement. The pulley 86 serves as a movable pulley to drive another tube 83 to move in the axial direction by cooperating with a chain, in such a manner that the circular three-segment telescopic structure can be driven to extend and retract.
Though the above configuration and structure is extendable and retractable, it still has the following disadvantages:
1. It is likely to cause internal damage: the three telescopic tubes 81, 82 and 83 are all designed in the form of a circular tube, the circular tube-shaped three-segment telescopic tube has no engaging restricting structure, such a design is likely to cause the damage to the inner structure due to the radial rotation and friction while the motor 84 drives the screw to rotate;
2. Linkage is likely to cause mutual interference: with the displacement of the pulley 86 at the top of the brace rod, the screw 85 utilizes the chain to drive the telescopic tube 83 to successively link with the telescopic tube 82 and so on, furthermore, between the bottom of the telescopic tube 82 and the screw 85 is disposed a restricting structure which causes the unnecessary interference during the pulling process of the restricting structure and the chain, thus affecting the complete extending/retracting operation.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.